This invention relates in general to environmental cleanup, and particularly relates to the recovery of non-aqueous phase liquids (NAPL) from subsurface formations.
The recovery of non-aqueous phase liquids (NAPL) from subsurface formations poses a significant technical and financial burden due to the inefficiency of recovering NAPL and due to the production of vast quantities of contaminated ground water during the recovery process. The prevailing pump-and-treat techniques are incapable of effectively addressing these issues and have therefore resulted in poorly designed recovery systems. Alternative techniques, such as soil vapor extraction (SVE) and vapor enhanced recovery, are not only costly but are also limited by subsurface conditions. Also, the ability to assess the efficiency of any recovery technique has been hampered by the complexities of subsurface operating conditions.
These factors can lead to an erroneous assumption that asymptotic recovery rates have been established despite the fact that significant hydrocarbons can still be recovered from the subsurface. By continuing these low recovery rates for an extended period of time, the overall cost of the recovery process increases dramatically. Environmental restrictions on the disposal of contaminated ground water pose an additional financial burden on the industry.
The end result is that the prevailing conventional recovery processes, over the long term, produces mostly water and dismal amounts of product. These inefficiencies are present not only in shallow environmental recovery processes but also in relatively deep mineral oil exploration processes.
In the case of shallow environment recovery processes, due to NAPL releases at conveyance, storage, and distribution facilities, the main goal is to economically recover the NAPL in order to limit environmental liabilities. However, the subsurface conditions are so complex that the prevailing technologies for removal processes can be significantly restricted. In addition, many of the current techniques prematurely reach asymptotic recovery levels, which significantly increases the cost of NAPL recovery. Several of the limitations caused by these restrictions include:
1) improperly designed subsurface collection sources that hinder the effective mobilization of the product;
2) variable water table elevations that render fixed intake pumps impractical, as the intakes are not ideally submerged in the NAPL;
3) techniques that use probes to position the intakes of dual phase pumps are not only labor intensive but ineffective to optimize the recovery process;
4) product recovery pumps equipped with hydrophobic membranes are also limited in its application as the membranes are subjected to chronic failures as in the case of biofouling;
5) total fluid pumps produce large amount of contaminated ground water in relation to the amount of NAPL collected, and
6) soil vapor extraction or vapor enhanced recovery processes are costly and limited in applications.
Therefore there is a need in the art to provide an improved NAPL extraction technique which not only enhances the recovery of NAPL but significantly reduces the recovery of water, and is easier to erect and maintain.
The present invention overcomes deficiencies in the prior art by providing an improved NAPL extraction technique which not only enhances the recovery of NAPL but significantly reduces the recovery of water, is easy to operate, and is easy to erect and maintain.
Therefore it is an object of the present invention to provide an improved NAPL extraction technique (NET).
It is a further object of the present invention to provide an improved NAPL extraction technique (NET) for the efficient recovery of NAPL from shallow subsurface formations.
It is a further object of the present invention to provide an improved NAPL extraction apparatus for the recovery of NAPL from shallow subsurface formations.
It is a further object of the present invention to provide an improved NAPL extraction apparatus for the efficient recovery of NAPL from shallow subsurface formations.
It is a further object of the present invention to provide an improved NAPL extraction apparatus for the effective recovery of NAPL from shallow subsurface formations.
It is a further object of the present invention to provide an improved NAPL extraction apparatus for the reliable recovery of NAPL from shallow subsurface formations.
It is a further object of the present invention to provide an improved NAPL extraction apparatus for the predictable recovery of NAPL from shallow subsurface formations.
Other objects, features, and advantages of the present invention will become apparent upon reading the following detailed description of the preferred embodiment of the invention when taken in conjunction with the drawing and the appended claims.